In situ photon transmission method was applied to study thermal phase transitions of t-carrageenan in CaCl(2) solution. Coil-to-helix (c-h) and helix-to-dimer (h-d) transitions were detected upon cooling. An extra dimer-to-dimer (d-d) transition was observed as well during cooling at low-temperature region. Upon heating only dimer-to-helix (d-h) and helix-to-coil (h-c) transitions were detected. Photon transmission intensity, I(tr) was monitored against temperature to determine several phase transitions and transition temperatures. It was observed that the c-h transition in i-carrageenan-CaCl(2) system performs a crossover between 3D percolation to classical theory. Upon heating, the specific heat exponent over the d-h transition was extracted from the transmitted intensity data and was found to be 0.045. (c) 2005 Elsevier B.V. All rights reserved.